(1) Field of the Invention
The present invention relates to an insulating material for the enameled wire used as a magnet wire of a motor of a refrigeration compressor. More particularly, the present invention relates to an insulating material for the enameled wire of a motor of a refrigeration compressor, which has excellent resistances to the hydrofluorocarbons and specific refrigerating machine oil used in the refrigeration compressor and moreover imparts deterioration resistance to said refrigerating machine oil.
(2) Description of the Prior Art
Dichlorodifluoromethane (CF.sub.2 Cl.sub.2) having no polarity has been mainly used as the refrigerant of the refrigerating cycle of electric refrigerators, refrigerating machines, air conditioners or the like; accordingly, a mineral oil type lubricating oil or the like has been mainly used as the refrigerating machine oil of said refrigerating cycle. Since the recent destruction of the ozone layer has prohibited the use of dichlorodifluoromethane containing chlorine atoms, only hydrofluorocarbons (hereinafter referred to as HFC) are coming to be used as a refrigerant.
HFC typified by HFC-134a, however, has poor compatibility with mineral oil type lubricating oils which have been used heretofore as the refrigerating machine oil, and there arises deposition of said lubricating oil at the low-temperature sites of the refrigerating cycle. As a result, the mineral oil type lubricating oil is not efficiently circulated in the refrigerating cycle, inviting reduction in lubricity and increase in wear of a compressor. Thus, a combination of HFC and mineral oil type lubricating oil is thought to have no practical applicability.
Hence, lubricating oils having at least one ester bond in a molecule such as ester-modified polyoxyalkylene glycol type, ether-modified ether type or ester type etc. (hereinafter referred to as synthetic lubricating oils) were proposed in place of the mineral oil type lubricating oils.
Meanwhile, HFC type refrigerants such as HFC-134a and the like are intended to be used in car air conditioners, electric refrigerators, etc. In electric refrigerators, (1) the refrigerating machine oil and the refrigerant both used therein are required to have good compatibility with each other; moreover, (2) since the motor is accommodated in the refrigerant system in most cases, it is necessary that the insulating material for covering the enameled wire, for example, the magnet wire of the accommodated motor, causes neither deterioration nor insulation breakdown and is stable over a long period of time.
However, the insulating materials currently used for covering the enameled wire of motors, such as formal resin, phenol-modified formal resin, polyester resin and the like, when placed in a refrigerant system using HFC type refrigerants, cause surface deterioration or peeling (blister or cracking) which result in their dissolution in the lubricating oil and/or refrigerant, etc., which invites poor insulation or insulation breakdown. Therefore, use of such an insulating material is not preferred.
Also, insulating materials such as polyamideimide, polyimide, polyester imide and the like, believed to have excellent performances, may undergo hydrolysis by the water contained in the synthetic lubricating oil used in combination with a substitute flon, to form an organic acid. The formed organic acid accelerates hydrolysis of ester bond in the synthetic lubricating oil molecule in a catalytic manner and causes deterioration of the synthetic lubricating oil; and this deterioration may invite reduction in refrigerating capacity. Thus, these insulating materials are not sufficient in quality.